Circuit maker and breaker devices having low electrical noise



Feb. 22, 1966 p, WATSON 3,236,986

CIRCUIT MAKER AND BREAKER DEVICES HAVING LOW ELECTRICAL NOISE Filed May 13, 1965 /nvem0r Percy K. Wmson,

is Afforney.

CIRCUIT MAKER AND BREAKER DEVICES HAVING LOW ELECTRICAL NOISE Percy K. Watson, Birmingham, England, assignor to General Electric Company, a corporation of New York Filed May 13, 1963, Ser. No. 279,866 6 Claims. (Cl. 200166) This invention relates to circuit maker andbreaker devices having a low electrical noise'feature, and more particularly, to circuit making and breaking devices wherein a radioactive material is added to the contact material to minimize electrical noise.

When an electrical circuit make and break device or switch is opened under non-ideal conditions, the switch contacts acquire an electrical charge which is due partly to the contact potential differences which exist between the separating surfaces, and also to sliding action which may occur during separation. This charge appears as undesirable circuit noise even under careful controlled conditions where it is rarely less than a few micro-micro coulombs and may be as great as several magnitudes larger. This type of electrical noise is a very undesirable item in sensitive circuits more particularly for example, a sensitive measuring circuit. As another example, electrical noise is an undesirable aspect in connection with a sensitive circuit input to an amplifier where the noise is also amplified. Furthermore, these noise levels may result in small spurious signals which may interfere with the performance of the overall system.

Accordingly, it is an object of this invention to minimize the electrical noise in electrical circuit maker and breaker devices. 7

It is another object of this invention to treat the contacts of circuit maker and breaker devices with a quantity of radioactive material to eliminate electrical noise.

It is yet another object of this invention to provide an electrical contact of an electrical circuit maker and breaker device having a source of a(alpha)-particles incorporated therein which is utilized to minimize noise.

It is another object of this invention to utilize a source of a-particle emanation on the contacts of a circuit maker and breaker device to equalize the charge potential in the circuit.

It is yet another object of this invention to add an rx-particle emitting isotope material in the form of polonium (Po to an electrical contact of an electrical circuit maker and breaker device to minimize contact noise.

Briefly described this invention includes incorporating a source of a-particle emanation in a pair of contacts in an electrical circuit maker and breaker device so that the various charges on the contacts leak away during the period when the contacts are beginning to separate and thus prevent electrical noise in the circuit. More specifically, this invention includes the addition of polonium 210, an a-emitting isotope, in the contact material of a circuit maker and breaker device.

This invention will be better understood when taken in connection with the following description and drawing in which:

The figure is an illustration of a measuring circuit utilizing the contacts of this invention.

It has been discovered that if one of the contacts of an electrical maker and breaker device is treated with an a-emitting source, that the switch may then be employed in very sensitive circuits and the background noise from switch operation is considerably reduced. Ordinarily, this background noise or electrical noise is caused by electrical charges of opposite polarity being accumu- 3,236,986 Patented Feb. 22, 1966 lated on the surfaces of the switch contacts. These charges may be caused by current flow through the circuit, interruption of the circuit, and also by sliding which may occur between the switch contacts during their separation.

Referring now to FIG. 1 there is illustrated an exemplary electrical circuit maker and breaker device 10. Device 10 includes a pair of contacts 11 and 12 which may be connected into a suitable electrical circuit and be referred to as a positive contact 11 and a negative contact 12. These contacts 11 and 12 are so mounted and positioned that they may be moved into engagement so that surfaces 13 and 14 contact each other to make or break an electrical circuit. A simple electrical circuit which has been utilized in the practice of this invention to measure electrical noise is also illustrated in FIG. 1 as circuit 15. Circuit 15 includes a pair of capacitors 16 and 17 of microfarad capacity and a sensitive electrometeror voltmeter 18 connected in parallel to each other. The capacitors are employed only to simulate a desired circuit having this capacitance. An electrical circuit maker and breaker device 10 as described is connected into the circuit of FIG. 1 between the capacitors 16 and 17. A resistor 19 of 10 ohms resistance is also connected across the switch to equalize the circuit. An electrical ground 20 is also provided for this circuit. In operation of the circuit, the switch 10 is operated at regular intervals. As a result of this practice, electrical noise appears as random voltages across the electrometer 18.

As one example of the practice of this invention in the noise level measuring circuit 15 of FIG. 1, the switch contacts 11 and 12 were carefully cleaned and the above-described operation indicated a measurable noise on the electrometer of about 1 millivolt. Thereafter,

surfaces 13 and 14 of both contacts were rubbed with a source of polonium 210 until the contacts indicated measurable radiation from the polonium 210. The strength of the radioactivity from this OPPaItlClC emitting source was found to be less than about 0.5 microcurie while the contacts indicated about 100 counts per minute radioactivity of an alpha particle survey meter. A reduced noise level of about 0.5 millivolt was obtained with the switch modified in this manner.

The addition of an tat-particle emitting source to the contacts of an electrical circuit maker and breaker device provides a marked reduction in'the noise level in the circuit. However, where a radioactive source was placed adjacent the contacts, the measured noise level was very high. Thus the amount of the tat-particle emitting material to be added to the contact material must be substantially less than that amount which would by itself cause a noise level equal to or greater than the noise level found in the circuit. Good results have been obtained in the practice of this invention where a sufiiciently large concentration of a-particle emitting material is added so that the radioactivity of the source is in the range of 0.01 to 1 microcurie units.

Several other examples were attempted utilizing B-emitting particles from such materials as U 0 but with relatively unsatisfactory results. However, other tat-emitting radio-active materials such as barium, radium, etc., will provide the marked reduction of noise level. Because of the relative availability, economy, and safety, it has been found that polonium 210 is a preferred u-particle emitting material for the practice of this invention.

Various methods may be utilized or employed toadd the tat-particle emitting source to the contacts of an electrical circuit maker and breaker device. It is preferred, however, to apply an a-emitting isotope to the surface of a clean contact. In one instance, in treating the silver contacts of a relay device, the contacts were first cleaned with acetone.

Polonium 210 was then deposited on the contact from a polonium nitratesolution of about .1 microcurie strength. The deposition was carried out by utilizing a drop of the solution from a pipette directly on contact material and thereafter removing the residue. The measured radioactivity of the contact material after this treatment was indicated about 300400 counts per minute.

Another example of the treating of silver relay contacts included first,-cleaning the contacts with acetone and then with HNO Polonium was deposited directly from a polonium nitrate solution having radioactivity 10 microcurie units as above described. The relative radioactivity .of the contact material was measured and foundto be milliamps, and 1.2 amperes for the relay with contacts of 300400 c.p.rn. and .55 ampere for the relay with contacts indicating about 1000 c.p.m. Under these condi- .tions best results were obtained at contact radiation levels of less than about 500 counts per minute as measured with an alpha particle survey meter. This further substantiates thepreferred practice of keeping'the radiation level of the contacts substantially below that point where the shot noise from the radioactive particles themselves exceeds ordinary contact noise.

The a-particle emitting material may be deposited on either the cathode or the anode, depending on the particular' conditions of the circuit. Results of this invention indicate that the addition of the a-particle emitting material to the cathode is preferred as a choice between the two contacts, and that usually both contacts are so treated. Polonium 210 is easy to deposit on various highgrade contact materials, such as silver, gold, and platinum. Methods of applying polonium may include electrochemical methods, i-.e., battery, or electrochemical deposition using a more active metal, such as from a chloride solution. For example, polonium will deposit on a strip of copper, silver, or bismuth which is dipped into the solution.

The action of the a-particleemitting sourceis to provide sufiicient ionization about a pair of make and break contacts so that static electrical charges on the :contacts are dissipated and the contacts are-brought to the same potential. With the use of the a-particle' emitting source as described the noise level is reduced. Application of not desired that the invention be limited to the particular description nor to the. particular configurations illustrated, and it is intended by the appended claims to cover all modifications within the spirit and scope of this invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. Anelectricalcontact-element for use in an electrical circuit make and break device, said contact element having a quantityof an a-pa'rticle emitting source occupying at 'least aportionof'the contact surface thereof, said source having radioactivity .ranging from about 0 .01 to about 10 microcurie units.

2. An electrical contact element substantially as re- .cited in claim 1 wherein the a-particle emitting source is the isotope polonium 210.

3. In an electrical circuit make and break device having' a plurality of electrical contacts arranged for relative movement into and out of contact with each other, the improvement comprising a quantity of an u-particle emitting source located over at least a portion of the surface of at least one electrical contact, said u-particle emitting source having a degree of radioactivity ranging from radioactivity eifective to dissipate static electrical charges from the electrical contact to radioactivity of about 10 microcurie units.

4. 'Anelectrical circuit make and break device comprising in combination, a pair of electrical contacts arranged forrelative movement in and out of-contact with each other, each of said electrical contacts having an aparticle emitting source occupying at least a portion of the contact surface thereof, said source having radioactivity in the range of from about 0.01 to about 10 microcurie units.

5-. The electrical make and back device substantially as recited in claim 4 wherein said contacts include silver as a contact material.

6. The method of treating an electrical contact element to provide for the automatic dissipation of static electrical charges from the contact-surface thereof comprising the steps of:

(a) cleaning the contact surface, and

(b) depositing on the clean contact surface a solution of an a-emittingisotope to produce a source thereon having a degree of radioactivity in the range of from about 0.01 to'a-bout l0 microcurie units.

References Cited by the Examiner UNITED STATES PATENTS 3,014,110 12/1961 Cobine 200-166 KATHLEEN 'H. CLAFFY, Primary Examiner. BERNARD A. GIL HEANY, Examiner.

H. O. JONES, Assistant Examiner. 

1. AN ELECTRICAL CONTACT ELEMENT FOR USE IN AN ELECTRICAL CIRCUIT MAKE AND BREAK DEVICE, SAID CONTACT ELEMENT HAVING A QUANTITY OF AN A-PARTICLE EMITTING SOURCE OCCUPYING AT LEAST A PORTION OF THE CONTACT SURFACE THEREOF, SAID SOURCE HAVING RADIOACTIVITY RANGING FROM ABOUT 0.01 TO ABOUT 10 MICROCURIE UNITS. 